Someone asked Albert Einstein at a party: "Oh, you are Albert Einstein, could you please explain me your relativity theory in three or four sentences?"

Einstein thought for a while, then he said, "I am very sorry, it is not really possible to explain relativity theory so quickly, but I will at least try to explain you why this is so.

Once I went for a walk with a blind man on a warm summer afternoon. After a while we came to a restaurant and sat down at a table. I asked him, 'Would you like a glass of milk?' 'I know what a glass is,' the blind man said, 'but what is milk?'

'Milk is a white fluid,' I replied.

'Aha, I know what a fluid is,' he said, 'but what is white?'

'White is the color of swans,' I explained to him.

'I know what a color is, but what are swans?'

'Swans are big birds with a crooked neck.'

'Oh, birds,' the man exclaimed, 'I have heard of birds. And what is crooked?'

I took his arm, stretched it and said, 'This is straight.' Then I bent it and said, 'and this is crooked.'

The man's face turned into a happy smile and he said, 'Now I finally know what milk is.'"